ARRL Satellite Bulletin ARLS005 (2001)

SB SPACE @ ARL $ARLS005
ARLS005 AO-40 Team Starts Slowing Spin Rate
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Space Bulletin 005 ARLS005
From ARRL Headquarters
Newington, CT March 9, 2001
To all radio amateurs
SB SPACE ARL ARLS005
ARLS005 AO-40 Team Starts Slowing Spin Rate
Initial efforts to slow AO-40's spin rate have been successful.
Peter Guelzow, DB2OS, of AMSAT-DL and the AO-40 team says
magnetorqueing has been able to decrease AO-40's initial spin rate
from 17.59 RPM to 15.9 RPM. ''The target is something in the area of
5 RPM,'' Guelzow said this week.
The onboard magnetorqueing system--which consist of solenoid
coils--makes use of Earth's magnetic field to control the
spacecraft's spin and orientation. Magnetorqueing is most effective
when Earth's magnetic field is strongest, so it typically only takes
place at perigee--when the satellite is closest to the Earth. Ground
controllers have been making incremental adjustments during each
perigee.
Guelzow said that as soon as the spin is favorable, AO-40's attitude
will be adjusted to improve communication with Earth. De-spinning
the spacecraft is a necessary first step to making any attitude
adjustments, however.
Guelzow said the onboard YACE camera was used to take some
photographs ''for a quick attitude determination,'' but he said the
digital photos were inconclusive. Additional pictures are planned
once the spin rate is reduced and communication more reliable.
The AO-40 S-band (2.4 GHz) transmitter is active and transmitting
telemetry as recovery efforts continue. When it met in Orlando late
last month, the AMSAT-NA Board of Directors recognized that
completing a full evaluation of AO-40 would take some time and that
all of the satellite's designed functions may not be available.
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